1 88 NEEDHAM. [VOL. I. 



quent approximation of hypoderm cells and basement membrane 

 (due, shall \ve say, to the drawing in of the peaked processes ?), 

 together with the loss of distinct cell boundaries in the hypo- 

 dermis, renders the relation of parts much less clear in the later 



stages. 



The tarsal claw and the tibial scrobe are developed alike from 

 thick projections of hypodermis cells, forming at first a blunt 

 point, which becomes sharp and takes on its characteristic tenac- 

 ular curvature only when the chitine begins to harden. The 

 corbel, however, being formed not at an angle of the leg, but 

 upon an originally smooth surface, develops differently. There 

 is a dense heaping of the hypoderm cells along what is to be the 

 rim of the ^/-shaped corbel, among which the very large mother- 

 cells of the fringing spines are early differentiated. Within the 

 rim the cells are few, slender, and scattered. Outer (cuticle) and 

 inner (basement membrane) surfaces are at first parallel ; but 

 the subsequent settling down of all the hypoderm cells upon 

 their basement membrane leaves, where the few slender cells 

 were within the rim, the proper concavity of the corbel. 



IV. Fat. 



The extraordinary growth taking place during the last larval 

 stage is due almost wholly to the accumulation of fat. This 

 occurring chiefly upon the dorsal side brings about the charac- 

 teristic curvature of the larva. Hardly has growth been com- 

 pleted, however, before the reverse process sets in ; the fat 

 begins to be demolished and used in the construction of new 

 parts. The external appearances accompanying the reduction 

 of the fat have already been described. In sections the appear- 

 ance is that of local disintegrations of the periphery of certain 

 of the fat masses. Fig. 8 is a section through the middle of 

 the thorax very near the beginning of metamorphosis. At the 

 bases of the budding appendages and immediately above and 

 below the alimentary canal, the fat is disintegrating. The ap- 

 pearance is that of the melting of frost. The fluid residuum flows 

 forward into the head and laterally out into wings and legs, 

 bearing along floating islands broken away from the fat masses. 



